System for electro-optical transmission of image



0. 8. 1940. Y. WA ET-A'L SYSTEM FOR ELECTED-OPTICAL TRANSMISSION OF IMAGE Filed March 13, 1937 INVENTORS YASUJ'l/FO IV/WA MASATSl/GU' IIOBAMSH/ 724/11! HAWIS/f/ ATTORNEY I I Patented Oct. 8, 1940 UNITED STATES SYSTEM Foeanccrno orricnpirasns- MISSION or IMAGE Iasujiro Niwa, Masatsugu Kobayashi, and Taku Hayashi, Mita, Shibaku, Tokyo,'.!apan, assignors to International Standard Electric Corporation, New York, N, Y., a corporationofDelaware Application March 13, 1937, Serial No. 130,632 In Japan March 28, 1936 1 Claim.

This invention relates to a system for electrooptical transmission of images of the type adapted to produce a carrier frequency by causing the sectional area of a scanning light flux to change at a high speed under control of an interrupting means. It is an object of the present invention to simplify the modulating action due to the picture surface tone or colour, of a light flux to produce a modulated carrier wave for a picture transmission or similar system, and to prevent the inclusion of unnecessary and injurious side band frequencies.

Fig. 1 shows one practical type of picture transmission system embodying this invention Fig. 2 shows the relation between the direction of change of a luminous spot area and the direction of rotation of a picture cylinder,

In these systems, it is intended first to obtain a modulated carrier light flux due to the tone or colour of an objective surface by scanning said objective surface with a light flux which is modulated at a high frequency, and next to change the completely modulated light flux into a corresponding current with a translating device, for transmission. In accordance with this invention, a system for electro-optical transmission of image is obtained which is adapted to improve the transmission efiiciency in time of the transmission of picture currents over a line and to lower the frequency band of transmission current and in addition to have no distortion produced upon the transmitted waves.

This invention may be most effectively used in conjunction with a line adapt-ed to transmit a frequency band of from a few hundred cycles to two or three thousands cycles, for example, such as an ordinary telephone line. In a picture transmission or similar system, it is necessary to select the carrier frequency and the number of picture elements for scanning per unit time so that the band of image currents to be produced and the lower side band of the modulated carrier wave may be filtered and separated perfectly without the superposition thereof. Hence in order to provide a picture transmission or similar systems which operates at high transmission efficiency and has good transmission characteristics in conjunction with an ordinary telephone line as described above, it is necessary to have a lowering of the carrier frequency, as the result of which it is clear that it is necessary that both side band waves produced are kept narrow.

This invention is intended to produce an electro-optical system which satisfies said requirement. The detailed description will now be given relating to one example of a picture transmission as shown in the drawing. l is a sending cylinder to which a picture to be transmitted is attached around its periphery, this cylinder being rotated at a low speed in the direction of the arrow, 2 is a light source and the light which is produced from said source is caused to form a focus upon the cylinder by a suitable optical system such as the lens 3, 4 and the light control plates 5, 5 so as to form the most effective flux of light, 6 is a rotating toothed disc adapted to vary and interruptthelightflux by its peripheral teeth, at a suitable place in the path of said light being rotated at right angles thereto. In this case, the rotating direction of said rotary disc is selected so that the direction in which the scanning spot is caused to vary depending upon the interruption thereof by the toothed member of said rotary disc, and the direction of rotation of the cylinder I coincide with each other. In other words, the arrangement is such that the light flux is interrupted in a given direction at all times Joy the rotation of the toothed member, so that the shape of the scanning spot upon the cylinder is caused to vary from its zero area to maximum and next from maximum to zero in a direction of change coinciding with the rotary direction of cylinder, that is the reverse direction of scanning. Fig. 2 shows this relation. In this figure l is a picture face upon the cylinder, a plurality of parallel dotted lines thereupon showing the path of the scanning line and an arrow 8 shows the rotating direction of cylinder, that is, the reverse direction of scanning. The toothed member with oblique lines shows the acting relation of the toothed rotating disc to the luminous spot and an arrow 9 shows the moving direction. A small circle II] shows the luminous spot upon a scanning line, said luminous spot, in scanning, being interrupted and varied by the movement of the teeth so as to decrease its area gradually from the lower part to the upper part and at least to zero and next to increase the area gradually up to maximum.

By the arrangement and operation of the system of this invention as described above, the change of a luminous spot is always caused to follow in the moving direction of the picture surface, and hence the result is that the scanning action is performed comparatively slowly, which reduces the generation of a transient phenomenon action to a great extent and prevents the wide distribution of the side band current wave which is produced in the translating .device. Also since no sudden change of a current is given in the wave-filter, no natural oscillations are set up and hence the generation of unnecessary vside band wave, thereby giving a comparatively narrow side band. But, if, on the contrary, the direction of change of the luminous spot is made to coincide with the direction of scanning, in opposition to the direction of movement of the picture, the change of picture surface due to the carrier wave action is so sudden that it produces a large transient phenomenon upon the generated current. This gives unnecessary interference within the wave-filter and causes the distribution of the side band wave over a wide range, which results in the extension of both side bands and makes it difiicult to transmit the picture currents at a high efiiciency over a telephone line.

What is claimed is:

An electro-optical transmission system comprising means for causing a scanning beam to move over a picture surface and means for producing a carrier frequency therefrom comprising means for periodically interrupting said scanning beam by intercepting said beam in the reverse direction of the motion of said beam with respect to said picture surface. 

